Disable nightly builds

We don't use nightly builds for fatimages anymore, removing the nightly schedule to not waste resources.

Still allowing workflow dispatch as we might revisit at some point.

Author: bertiethorpe

.github/workflows/nightlybuild.yml

@@ -10,8 +10,8 @@ on:
             - LEAFCLOUD
             - SMS
             - ARCUS
-  schedule:
-    - cron: '0 0 * * *'  # Run at midnight on default branch
+  # schedule:
+  #   - cron: '0 0 * * *'  # Run at midnight on default branch
 
 jobs:
   openstack: